This invention relates to a method for the controlled ink-jet spreading of polymers for insulation and/or protection of printed circuits, according to the preamble of the main claim.
1. Technical Field
The method finds particular and useful application in the manufacturing processes of printed circuit electronic cards.
2. Background Art
At present various manufacturing methods are known for printed-circuit electronic cards.
Particular reference is made here to the cards made up of a sheet of plastic material for example plastic reinforced with fiberglass with a layer of electrically conductive material placed on the surface such as, for example, copper, said sheets being later cut into the dimension and profile of the desired card.                The copper surface is then subjected, using different techniques (curtain coating, sprinkling, etc.), to the deposition of the printed circuit design.        Subsequently the exposed external surface of the copper layer is removed, for example, with a chemical process to obtain the electronic printed circuit.        Followed by stripping, namely the removal of the protection of the design previously deposited on the printed board (card).        Finally, the spreading of a protective insulating polymeric layer takes place.        
This deposition of the protective insulating polymeric layer on the printed card or board is carried out with different techniques, generally sprinkling or curtain coating.
The spreading of the layer on a stepped/engraved surface (the level of the printed board is higher than the level of the plastic surface of the card for the value of the copper layer of approximately 45 microns) involves the need to apply a substantial protective insulating layer, otherwise the corners of the circuit conductor lines might remain exposed and therefore render the card defective.
The total protection thickness implies therefore a maximum deposition of 60 microns with evident material wastage.
The result of the cards obtained is not, however, always of the highest quality and precision due to the inevitable overflow of the deposited liquid material.
The overflow is furthermore inevitable because the metal is not as absorbent as paper and despite the porosity of the plastic material it is not as high as that of the paper and for this reason it is very difficult to obtain sharp defined outlines.
Furthermore, these insulating and protective materials are expensive.
The system for covering and protecting the cards by means of silk screening is also known. However, this method is very slow and involves the use of notable material and does not allow adequate quality and precision to be obtained.
EPO 930641A (Seiko Epson Corp.) disclosed a “Pattern Formation Method and Substrate Manufacturing Apparatus”.
In this document (column 15, line 40-column 16, line 20), it is disclosed the use of “ . . . forming banks—in the form of dikes—that inhibit the outflow of fluid near the borders of the pattern-forming region as a physical-chemical action, . . . ”. The suggested system uses, on a single advancing printing action (FIG. 10), the formation of both banks (706) with a first treatment apparatus (306), immediately followed by an ink-jet print head (2) that ejects the ink fluid droplets (11-12) inside the pattern-forming region delimited by said banks (706). A plasma ashing, etching, or another method for bank removal is further used. The bank material (polyamides, acrylic resins, epoxy resins and the like) being conceptually different from the following ink droplets (12).
This solution has the disadvantage of using:
two deposition apparatus, one following the other (306, 2);
two different materials, one for the banks (706) and one for the main scope of the printer, namely the liquid ink (12);
additional bank-removal head following pattern-fixing (line 18-19, column 16) or a following treatment apparatus (310) by rubbing, returning the overflowing portions back to the confines of the pattern-forming region and forming a pattern (15) of a specific width (line 41 to 53 of column 16).